I don't view it as a one time choice at all (if I had to pin down the point at which you made a choice, I would say mine had already passed). My point is that choosing what you do from day to day is important.

Very few people spend a lifetime doing pure research.

This appears to be true only insofar as academia is small. I know a great many people who have spent their entire lifetimes doing pure research, a great many people who are basically guaranteed to spend their entire lifetimes doing pure research, and a great many people who plan to spend their entire lifetimes doing pure research.

The people who contributed most to society did not consciously set out to do so at the start of their careers.

I think this is weak evidence for your implicit conclusion. I have to choose, for example, what I do tomorrow. Do you think that by being concerned with the effects on society I contribute less?

I don't have time right now, but perhaps I will dig through some biographies later tonight. It is certainly an interesting exercise.